1. Field of the Invention
The present invention relates to a sheet conveyance apparatus that can correct a skew of a sheet that is conveyed obliquely with respect to a sheet conveyance direction to a direction along the sheet conveyance direction, and an image forming apparatus including the sheet conveyance apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a multifunction peripheral thereof generally includes a function of forming an image on a sheet and a function of reading a document. Then, a technique, concerning skew correction of a sheet and a document to be conveyed in order to improve accuracy of image formation and document reading, has been discussed.
In the above-described conventional skew correction, there is a method by which the skew correction is executed by striking the downstream end of a sheet in a sheet conveyance direction to a nip portion on a stopped registration roller pair to form a loop. This is a method to strike the downstream end of the sheet in the sheet conveyance direction against the nip portion on the registration roller pair, which extends in a direction orthogonal to the sheet conveyance direction to form the loop, thereby aligning the downstream end of the sheet in a direction orthogonal to the sheet conveyance direction. Thus, after a skew has been corrected, the registration roller pair is rotated, thereby causing the sheet, the skew of which has been corrected, to be conveyed.
However, the downstream end of the sheet in the sheet conveyance direction is struck against the nip portion on the registration roller pair, thereby securely correcting the skew of the sheet. However, it causes a collision noise.
Thus, there is a method to detect the downstream end of the sheet in the sheet conveyance direction by a detection unit disposed in the vicinity of the downstream in the sheet conveyance direction of the registration roller pair to once stop the conveyed sheet directly before the registration roller pair. This drives a conveyance roller on the upstream in the sheet conveyance direction in advance after the sheet has once been stopped, thereby abutting the sheet on the registration roller pair to form the loop. Thus, the skew of the sheet is corrected. At that time, since the sheet is struck on the registration roller pair before the conveyance speed of the conveyance roller is increased, the collision noise is reduced (refer to Japanese Patent Application Laid-Open No. 6-127753).
As described above, in the conventional skew correction, from the viewpoint of miniaturization and low cost, a method is used which strikes the downstream end of the conveyance sheet on a registration roller pair or a skew correction member. However, as described in Japanese Patent Application Laid-Open No. 6-127753, in order to reduce a collision noise in striking, if conveyance of a sheet is once stopped to reduce a speed, productivity is decreased. Further, because an amount of loop is constant, when a rigidity of the conveyance sheet is high, the conveyance roller may slip after the sheet is struck on the registration roller pair. As the necessary amount of loop for skew correction is not secure, excellent skew correction may not be realized.